Field of the Invention
Embodiments of the present invention generally relate to a liquid discharge head and a liquid discharge apparatus, and more particularly, relate to a liquid discharge head in which an electroconductive protective film provided on a heater which generates heat upon application of a voltage for discharge of a liquid, such as ink, is provided in common to plural heaters.
Description of the Related Art
In an electroconductive protective film formed on plural heaters arranged on a substrate which constitute a liquid discharge head, a common pattern of an electroconductive protective film corresponding to plural heaters is often used. An electrical leakage check between an electroconductive protective film and a heater wiring layer is performed, for example, as an examination after the manufacture of a substrate. The electrical leakage check is performed for the following reason. If an electrical leakage occurs between the electroconductive protective film and a heater wiring layer, oxidization and dissolution of the electroconductive protective film caused by an electrochemical reaction between the electroconductive protective film and the ink due to an influence of a potential for driving the heater drive potential may proceed, and a change in discharge characteristics and defective discharge may be caused. By using a common pattern of the electroconductive protective film, the electrical leakage check on plural heaters can be performed collectively, and therefore the examination can be simplified.
As a form of using a common pattern of an electroconductive protective film, Japanese Patent No. 4995355 describes a configuration of removing kogation adhering on the electroconductive protective film upon discharge of ink by applying an appropriate potential for the electroconductive protective film on the heater and controlling an electrochemical reaction between the electroconductive protective film and the ink. Also in this case, the electrical potential of the electroconductive protective film on plural heaters can be collectively controlled as an electrically common pattern.
In the configuration in which the electroconductive protective film is used in common to the plural heaters, if a leakage occurs between the electroconductive protective film and the heater wiring layer immediately after the manufacture of the substrate, the leakage can be detected in an electrical check before the assembly of the substrate. Therefore, a chip with a leakage can be excluded as a defective chip.
There is a possibility, however, that a leakage may occur in a substrate due to a thermal and mechanical impact etc. during assembly into a discharge head even if the substrate has no leakage immediately after the manufacture of the substrate. Further, even if no leakage occurs after the assembly into the discharge head, a leakage may occur due to a thermal impact, cavitation, etc. during usage of the discharge head for recording, etc. In a configuration in which the electroconductive protective film is used in common to the plural heaters, if a leakage occurs in at least one of the plural heaters, an electrochemical reaction may proceed in the electroconductive protective film on electrically connected other heaters. As a result, a change in discharge characteristics and defective discharge may be caused in nozzles corresponding to these heaters.